1. Field of the Invention
The present invention generally relates to a pneumatic tire, and specifically relates to a pneumatic tire for use on ice and snow.
2. Description of the Related Art
Pneumatic tires for use in winter is required to have good performance on both ice and snow. One approach to improve the performance on ice is to make small a ratio of a groove area to a ground contact area of a tire. However, simple reduction in this ratio leads to a decline in performance on snow and in the capacity to prevent hydroplaning. Consequently, it is difficult to have good performance both on ice and snow in one tire.
Japanese Patent Laid-open Publication No. 2000-225814 discloses a conventional pneumatic tire. The conventional pneumatic tire includes a pair of wide first main grooves that runs around the circumference of the tire; a central land parted with the first main grooves in a central region on a tread; a pair of second main grooves that extends on outer sides of the first main grooves in the direction of a tread width to form lateral lands between the first main grooves and the second main grooves; and a plurality of transverse main grooves that opens to the first main grooves via the second main grooves from ends of the tread. The central land includes a series of blocks around which are arranged a plurality of narrow transverse sub-grooves that opens to the first main grooves. Each of the lateral lands includes a circumferential narrow groove that runs around the tire. The lateral land includes a series of outer blocks on the outer side in the direction of the tread width and a series of inner blocks on the central side of the tread on each side of the circumferential narrow groove. Each series of the blocks include sipes. The inner blocks of the lateral land include sipes that are equally angled in a certain direction on each tread, and notched with an angle reverse to the transverse main grooves. The other blocks include sipes that are notched in substantially parallel to the transverse main grooves.